Lithiation of 2-aryl-2-(chloroaryl)-1,3-dioxolanes and its application in the synthesis of new ortho-functionalized benzophenone derivatives

摘要

2-Aryl-2-(chloroaryl)-1,3-dioxolanes 4 were lithiated ortho to the ketal group of the chloroaryl ring by treatment with butyllithium in THF between -78 and 0 degreesC. The site selectivity of some of the deprotonation reactions was rationalized by the long-range effect of the 4-chloro substituent. The lithio species thus generated were treated with various electrophiles to give ortho-functionalized benzophenone derivatives. Intramolecular competition between the aryl rings was observed in the lithiation of 2-(4-chlorophenyl)-2-(4-fluorophenyl)-1,3-dioxolane (4s). (C) Wiley-VCH Verlag GmbH Co.